1. Field of the Invention
This invention relates to cooling of integrated circuits and, more particularly, to the use of cooling ducts alone or in combination with cooling fans to lower the temperature of integrated circuits.
2. Description of the Relevant Art
The reliability of electronic equipment has typically been associated with the operating temperatures of its components. In general, the higher the temperature the less reliable the component. With the continuing emphasis on miniaturization and enhanced performance of electronic devices, the density of electronic components per unit volume, and hence the power density, are steadily increasing. This tends to cause elevated temperatures due to heat dissipation problems. Since the elevated temperatures lower the performance of integrated circuits, there is a need for effective cooling devices.
The operating speed of an integrated circuit tends to be dependent on its temperature. As the temperature increases the effective operating speed of the integrated circuit is lowered. The operating temperature of an integrated circuit in a computer system is typical influenced by the operating speed, the voltage usage and the temperature of the interior of the case. Assuming no changes are made to the operating voltage of the integrated circuit, a process which lowers the temperature of an integrated circuit and/or the temperature of the case may allow optimal performance to be obtained for that integrated circuit.
Various heat dissipating apparatus, including fans, thermal control circuits, heat sinks, cooling couplers, etc. have been developed and extensively used in computer systems. The most commonly used of these devices is the cooling fan. Cooling fans are typically used to create an air flow through the computer case. Despite the presence of a cooling air stream the temperature within the computer case or chassis still tends to rise. The temperature rise may be caused, in part, by the insufficient volume of cooling air flowing through the computer case. Under typical usage, the interior of a computer case may extend upwards of 40.degree. C., for example.
One cooling system involves blowing heated air away from the hottest integrated circuits. As an integrated circuit becomes hotter the air in the immediate vicinity becomes warm. A fan is typically mounted onto the integrated circuit and is used to blow the heated air away from the component, thereby lowering the temperature of the component. The air leaves the vicinity of the integrated circuit and is circulated throughout the computer case. Heated air within the computer case tends to cause the temperature of the other components to rise. Typically, the highest temperature components, such as central processing units, are cooled in this manner.
Other cooling systems tend to use a combination of direct component cooling along with an external air stream passing through the computer. In this type of system the integrated circuit is cooled by directly blowing the heated air from the integrated circuit into an air stream. By placing one fan on the integrated circuit and the another fan near the integrated circuit, the dissipated heat may be more efficiently removed.
Additionally, a heat sink, typically composed of a series of metal fins, may be attached to a high temperature integrated circuit to aid in cooling. Cooler air may be drawn across the heat sink by fans mounted on the walls of the case or on top of the heat sink. Such a system tends to cool a component by allowing the heat sink to draw the heat away from the component. The cooling air removes the heat from the heat sink and the hot air is blown outside the computer case.
Such a system, however, is insufficient to remove all of the heat from the case. The heat sink is typically placed next to the fan blowing air out of the case. Since the air typically enters the case from a side opposite the fan, the air is usually heated to a slightly higher temperature by other components within the system before reaching the heat sink. This lowers the efficiency of cooling such that the integrated circuit may not get an appropriate amount of cooling. Since the integrated circuit may not be totally cooled, the excess heat is typically dissipated throughout the case causing the temperature of the case to rise. In such systems the temperature of the case may be up to 10.degree. C. higher than the outside air.
It is therefore desirable to devise a cooling system that will cool the hottest components without the heat being dissipated to the other components. This should reduce the temperature of the computer case, since there will be less heat generated within the case. Additionally, the cooling system should transfer the cooler air to the component to be cooled without the air being heated by other components before reaching the component of interest.